Process for the working up of lead ores



May10,1938. -K,R HRE' 0 2,116,679

PROCESS FOR THE WORKING UP OF LEAD ORES Fil ed May 15, 1957 4 Sheets-Sheet l INVENTDR. KURT RUDOLF GOHRE ATTORNEY.

May 10, 1938. K. R. GOHRE 251,167,679

PROCESS FOR THE WORKING UP OF LEAD ORES Filed May 15, 1957 4 Sheets-Sheet 2 INVENTOR. KURT RUDOLF GOHRE BY G Am ATTORNEY.

May 10, 1938. K. R. GOHRE PROCESS FOR THE WORKING UP OF LEAD ORES Filed May 15, 1957 4 Sheets-Sheet 3 INVENTOR. KURT RUDOLF GOHRE ATTORNEY.

May 10, 1938. K. R. GOHRE PROCESS FOR THE WORKING UP OF LEAD ORE-S Filed May 15, 1957 4 Sheets-Sheet 4 74 lJllll I lllll ll' INVENTOR. KURT RUDOLF' GOHRE BY ATTORNEY.

Patented May 10, 1938 UNITED STATES PATENT OFFICE Kurt Rudolf Gohre, Frankfort-on-the-Main, Germany, assignor to American Lurgi Corporation, New York, N. Y., a corporation of New York Application May 13, 1937, Serial No. 142,425

In Germany May 16. 1936 12 Claims.

This invention relates to a process for the working up of lead ores.

Hitherto it has not been possible successfully to work up lead glance of the fine and very fine grain classes on the lead hearth by the roasting reaction method. The hearth working produces, even in the case of ores in lump form, a certain quantity of flue dust consisting principally of PbS, PbSO4, PbO and excess carbon, which quantity, however, is not so great that, after the flue dust has been converted to lump form by burning or sintering, it could not be completely returned to the hearth. Unless previously converted into lump form, the flue dust would at once be blown out of the charge material again. Fine materials, for example flotation ores, which generally possess a degree of purity and a lead content adequate for the hearth process, render the application of the hearth process impossible by the o fact that they give rise to excessive quantities of flue dust, even if they are first made into lump form or superficially agglomerated by known methods. In my co-pending application Serial No. 142,426 I have described a process for roast- 25 ing lead ores without the formation of excessive amounts of flue dust involving a reduction in the temperature of the charge by employing blast gases containing less oxygen than air.

Since on the one hand, a rapid and also non- 30 uniform heating of the material on the ore hearth, and on the other hand, complete alteration of same by chemical reactions occurs, the requirements which have been made with regard to the mechanical strength of fine ore which has 35 been previously converted into granular form by known processes, are unusually stringent, and hitherto it has not been possible to convert fine lead ores into lump form in such a way that they were able to satisfy these requirements. Super- 40 ficial agglomerated ores do not give satisfaction in this case because agglomeration of lead ores, that is to say, sintering same upon the blast grate, is tantamount to roasting same. Roasting naturally also occurs when only superficial agglomera- 45 tion is intended, because in this case also the sulphur content in the ore serves as fuel for the agglomeration. Since it is only possible to produce sintering by superficial agglomeration when the material is heated to high temperatures, in so this case also the consumption of fuel and consequently the degree of roasting is considerable. If an already roasted lead ore be worked up on the ore hearth, then the deficit of sulphur must higher working temperatures, which lead to an increased formation of flue dust and scorification and thus to lower yields. of lead. Moreover, it is no longer possible to work up all the flue dust together with fresh ore upon the ore hearth, so that the proposals hitherto made have not yielded a practical solution of the problem.

By means of the invention it is now possible to avoid the drawbacks of these proposals, and particularly the excessive formation of flue dust durm ing the metallurgical treatment of fine lead ores upon the ore hearth.

One object of the invention consequently is to prepare fine. lead ores for workingup on the ore hearth according to the roasting reaction process, 15 by converting same into agranular or lump form, said process being constituted so that the material in granular or in lump form behaves just as advantageously or still more so than ore which is naturally in lump form.

Another object of the invention is to produce the granular form by heating fine lead ores which have been brought into a granular or still less consolidated form in such a manner that subsequently losses of sulphide during heating did not occur.

A further object of the invention is the heating of fine lead ores which have previously been brought into a granular or still less consolidated form by means of hot gases containing less oxygen than air, and the utilization of such gases for heating as contain sulphur dioxide or carbon dioxide, or both substances.

Other objects and advantages will become ap-: parent to those skilled in the art from the following description taken in conjunction with the accompanying drawings, in which:

Fig. 1 is a more or less diagrammatic illustration of a process embodying the principles of the present invention; 40

Fig. 2 is a more or less diagrammatic illustration of another embodiment of a process in ac cordance with the principles of the present invention;

Fig. 3 is a more or less diagrammatic illustration of a further modification of a process in accordance with the principles of the present invention, and.

Fig. 4 is a more or less diagrammatic illustration of a further embodiment of a process in 9.0-

cordance with the principles of the present invention.

A plurality of bunkers I, 2, 3, etc. are provided above the conveyor belt 4. In these bunkers the fine sulfide lead ores are stored for use in the. r

process. When the necessary additions for the roastingreaction process, that is limestone and coal are to be mixed with the fine lead ores one of the bunkers may contain a mixture of coal and limestone or additional bunkers may be provided.

for limestone and coal. When flue dust which has been separated from the waste gases of the lead hearth is to be treated on the lead hearth one of the bunkers may be provided for receiving the flue dust. The fine lead ores and likewise the flue dust or limestone or coal or several of these materials are drawn out of these bunkers onto the conveyor belt I in appropriate amounts and conveyed to the mixer 5 where the individual components of the charge are well mixed and at the same time may be moistened. The mixture falls from the mixer through pipe 6 into the hopper I of the briquet press 8. 9 is the ,drive for the mixer which in turn is driven by belt H from a source of power l0. l2, I3, II and I5 are similar drives for the conveyor belt 4, the briquetting press 8, the conveyor belt [6 and fan I! respectively.

In the embodiment of the present invention depicted in Fig. 1 the briquets are conducted from the press 8 through the trough I8 to the conveyor band l6 which is completely encased by housing l9. In trough l8 freely swinging flaps 20 are provided which serve to hinder the fall of the briquets through the trough. The lead hearth may be of the Schlippenbach-Herd type described in U: S. Patent No. 2,018,242 and is represented schematically. The hearth comprises the annu lar rotating hearth 2| and the stationary hood 22 to which the blast air streams from pipe 23 through the. inlet pipe 24.

This lead hearth is built in a manner known per se. The waste gases from the hearth are led through the pipe 25 to the fan l1. and are forced by it through the pipe 26 into the housing IQ of the conveyor belt [5. Here the waste gases flow war the briquets which are situated on the conaeyor belt and thereafter are led through the pipe 21 to the waste gas canal 28. The briquets are thrown from the conveyor band Hi to the trough 29 which is also provided with swinging flaps 30 similar to those in trough It. The trough empties into the bunker 3| for the briquet through whose discharge 32 the lead hearth is charged.

In order to obtain particularly useful briquets, the speed of the conveyor band It is so arranged for example that the briquets are heated during their stay on the conveyor band for about 3 minutes at 350 C. In the pipes and troughs valves and dampers 33 can be provided in a known manner and in suitable number. In place of the conveyor belt l6 (of Fig. l), a shaft 40 is shown in Fig. 2. The shaft is provided with installations ll so' that the briquets falling out the trough iii are uniformly moved downwardly in this shaft. Also in this case, the waste gases from the lead hearth can be used for heating the briquets in theshaft 40. For example, the waste gases from the hearth are led through the exhaust pipe 25 to the manifold 42 from which the gases stream into shaft .40, through inlet pipes 43. The gases flow upwardly through the interstices between the briquets which fill the shaft and then into thepipe 44 to the waste gas canal 28 similar to that of Fig. 1. The waste gases can thus be sent to a dust precipitator of known type and likewise to a plant where its S02 content can be utilized.

In the shaft 40 the briquets are heated practically in the same manner as upon the conveyor belt I6. They fall through a discharge 45 of the shaft into a. conveyor device, for example car 46 and are then placed in known manner in bunkers in order to be fed into the lead hearth.

In the plant built according to Fig. 3, the bri-' quets pass from the press 8 first into a bunker 50 which is connected through the discharge device 5| with a shaft 52. This shaft, similar to the shaft III of Fig. 2 is provided with installations ll likewise for the purpose of uniformly and protectively controlling the downward movement of the briquets in the shaft. Two oppositely arranged side walls of the shaft 52 are provided with slits 53. 54 is the discharge device for the shaft.

The hot waste gases from the hearth flow into the distribution chamber 55 through pipe 25 from which they flow into the shaft 52 through the slits- 53. Here they flow as a transverse stream through the briquet charge and pass through slits 56 in the oppositely arranged wall into the collection chamber 51. They are sucked off from here by means of the fan I! through the pipe 58 and forced into the discharge pipe 26. The pipe 26 branches and leads through ii to the blast intake 24 of the lead hearth. Valve and damper devices 59 and BI] are provided in the pipe 26 beyond the branch and in the pipe 6|. These have the purpose of regulating the amount of gas conducted to the hearth according to the re quirements thereof. The operation of this device takes place in the manner already described for Figs. 1 and 2. The same mixing and pressing device can be used in Fig. 4 as described for the previous figures. The briquets go from the trough l8 onto a shaking trough III. A bunker H for coal dust is located above the latter. The coal dust is uniformly spread on the briquets by a discharge device 12 for example a rotating plate. Upon 100 parts by weight of briquets about2 to 4 parts by weight of coal dust are used. A good and uniform distribution of the coal dust on the surface of the briquets takes place on the shaking trough through the forward movement of the briquets which so to speak are powdered with coal dust. The shaking trough feeds the bunker by the fans 19 and 80 produces a further combustion of the coal dust. The speed of the combustion is so arranged that only-the coal dust adhering to the surface of the briquet is burned and appreciable reduction in the sulfur content of the briquet does not occur. The thickness of the layer of powdered coal on the briquet, the combustion and the amount of air drawn through the briquet are naturally correspondingly controlled and indeed are so arranged that the combustion of the coal dust is completed or substantially completed when the individual grates of the traveling grate leave the region of the vacuum box 16 and enter above the vacuum box 11. During the passage over the vacuum box H, the cooling of the briquets takes place for example in such a way'that very large amounts of air are drawn through the charge on the grate or other coal gases with oxygen content lower than that of the air may be drawn through. In this way, it is possible to heat the briquets to about 800 C. without going to too high a temperature and without the occurrence of an essential roasting away of the ore. After cooling, the briquets go through the discharge 18 to the conveyor device 46 and from the conveyor in known manner to the lead hearth for smelting to metallic lead. The waste gases from the traveling grate are conducted to a stack after cleaning by means oi the blowers I9 and 80. The waste gases, however, or a part thereof could be used as a blast air for the operation of the lead hearth either by themselves or together with fresh air. A source of power 8i is provided for driving the travelling grate by means of drive 82 and driven pulley 83. Blowers I9 and B are driven from the same source of power 8| by belts or'similar means 84 and 85 respectively.

It has been shown that fine ores can be worked up in just as advantageous manner, and often in still better manner than orein lump form, when they are first granulated with or without the addition of binding media, and subsequently heated in such a manner that subsequent losses of sulphide do not occur. This heating produces such a favourable consolidation of the individual lumps, that during the subsequent treatment on the ore hearth, formation of flue dust is kept within supportable limits, and the quantity of fiue dust formed can be directly returned to the ore to be treated.

During the process of making the ore into lumps, the necessary substances such as lime and coal, as well as the flue dust constantly forming and similar material, may be added to the fine lead ores. However, there is naturally nothing to prevent these and like substances being added in the same manner as in hitherto known methods.

For example, fine galena, with or without binding media, is mixed with-flue dust, lime and coal and worked up into small pressed pieces by means of a roller press or similar briquetting devices, or briquettes are made out of the fine ore by other methods. Sulphite lye, for example,

has given good results as a binding medium. It is also possible to use burnt or slaked lime and, as described hereinafter, to carbonate same again by treatment with waste gases containing carbon dioxide, whereby hard moulded pieces are obtained.

According to the invention the briquettes are now heated either for the necessary time to temperatures of about 200-400 C., or for a correspondingly shorter time to temperatures above about 400 C. If the heating temperature be kept below 300-400 C., the heating can be carried out in any desired manner. If these temperatures be exceeded during the heating, the oxidation already commences in the presence of air, 1. e. a portion of the lead sulphide passes into oxide with the formation of sulphur dioxide.

In order to prevent an undesirable roasting of the sulphides, according to the invention for example, the oxygen content of the gases employed for heating the briquettes is reduced to a certain extent to below the oxygen content of the atmosphere. For example, the oxidation is greatly reduced by using for the heating combustion gases which, for example, may be previously utilized in the usual manner, in order to reduce their temperature for example to 500-800 C. for any purposes, for example for steam raising. It is particularly convenient to use the waste gases of the lead hearth for the heating of the briquetted ore. The waste gases of the roasting reaction process, particularly when well enclosed hearths, for example Schlippenbach hearths consisting of a rotary annular hearth and a hood extending down to the outer periphery of the hearth and having a few small working openings therein, are used, contain adequate heat for effecting the solidification of the briquetted ore, which heat was hitherto not utilized. The waste gases also have a lower oxygen partial pressure than air, in consequence of their sulphur dioxide and carbon dioxide content. According to the invention therefore, the waste gases of the hearth are also passed over or through the briquettes.

This can take place by supplying the briquettes to the ore hearth on a conveyor resembling a travelling grate and passing the waste gases of the hearth through them in a direction at right angles to the direction of travel of the briquettes. Another way consists of allowing the briquettes to travel downwards in a shaft and to conduct the waste gases of the hearth through two side walls of the shaft which are provided with gratings, or to conduct the waste gases from top to bottom or vice versa through the charge material in the shaft which may then, for example, also have solid walls. In order not to draw in any false air, the charging and discharging apertures of the shaft must be provided with a gastight closure means. It has been found, in this arrangement, that the waste gases of the hearth, probably owing to the fact that they contain flue dust and sulphur dioxide, efiect a particularly good solidification of the briquettes. Other hot gases which contain sulphur dioxide or fiue dust or both substances also act in a similar manner, for example, the exhaust gases from blast grates, upon which ores have been sintered or roasted.

The solidification of the briquettes by heating is not, however, limited to the use of such gases. On the contrary, other gases poor in oxygen, for example furnace gases or hot roasting process 1 gases can also be used as heating agents, the

heating also taking place, for example, with the aid of the aforesaid travelling grates or shafts of the most diverse form. In the case of heating gases which still contain a certain amount of oxygen'which must naturally be lower than that of the atmospherethe sulphide contained in the ore can still react with said oxygen. This reaction however only takes place on the surface of the granulated ore. In these circumstances there is formed around each grain of ore a shell of great strength which likewise contributes to maintaining the roasting of the sulphide at a very low level so that only a very small portion of the sulphur in the ore is oxidized. This shell however, has the great advantage that it confers great strength on the granulated material, so that the latter behaves in a particularly advantageous manner upon the ore hearth.

The fine ore can also be, granulated or made into lump form and mixed with fuel, for example fiotation ores by damping, compressing and sifting, or brought to a definite grain size by other known means and dusted externally with a coating of fuel. The mixture of ore and fuel is then ignited and the fuel is burnt out, for example by passing air therethrough. For example, the mixture of flotation ore and fuel prevlously treated in the manner described is blown on asuction grate. It was found that in this manner the sulphur content of the galena is reduced only by a few per cent, but in any case is not reduced to such an extent that any fall- 7 excessive when they are used for the heating of the ore hearth. The hearth waste gases then new the briquettes and the roasting which then occurs during the heating is undesired, this can be avoided by maintaining a circulation of gas through the hearth and the heating device for said briquettes. For this purpose. the heating gases flowing out of the briquettes or a portion thereof are returned to the hearth. The gases,

preferably with the admixture of additional air, are blown through the tuyres into the charge on back to the heating device for the briquettes.

Before. or after the passage through the latter a portion of the gases is branched oil from the' circulation.

The repeated passage of the gases through the permits the economical working up of the outgoing gases to sulphuric acid or sulphur dioxide, or by way of concentrated sulphur dioxide to sulphurie acid or sulphur. This embodiment of the process according .to the invention has also a number of further advantages.

The hearth process works more economically,-

in respect of the additions of fuel and the requirements of metallurgical plant, than other methods. A disadvantage of the hearth process has, however, been the impossibility of utilizing the sulphur from the ores, since the waste gases had too low a sulphur content (0.05 to 1.5% S02) for them to be worked up into sulphuric acid, sulphur or $02. This disadvantage is eliminated by the present invention, which however not only solves the problem of rendering flotation ores suitable for the hearth process, but at ,the same time also ensures the utilization of their sulphur content.

Obviously various modifications may be made in the process as hereinbefore described. As already mentioned, it is possible to use other heating gases than the waste gases of the hearth for the production of the briquettes. It is also possible, for example, when briquetting to omit the addition of coal or lime or also flue dust, if the latter can be put to other uses or if it be preferred to burn or sinter it separately. If, for example, no fine coal is available and it be desired to avoid the expense of comminution, both for coal and for lime, it is reasonable to add these substances to the hearth charge direct; although substantial advantages generally accrue otherwise from the actual thorough mixing of these additions with the ore.

I claim:-- I

1. A process for converting finely divided lead ores into lump form for metallurgical treatment on the ore hearth by the roasting reaction method, which comprises granulating said fine lead ores to form granules and heating said granules to a temperature below the melting point of the granules in such a manner as to Prevent any substantial combustion of the sulphur contained in the ore.

2. A process for converting finely divided lead ores into lump form for metallurgical treatment on the ore hearth by the roasting reaction method, which comprises granulating said fine lead ores to form granules and heating said granules to a temperature below the melting point of the granules with gases containing less oxygen than the air.

3. A process for converting finely divided lead ores into lump form for metallurgical treatment on the ore hearth by the roasting reaction method, which comprises granulating said fine lead ores to form granules and heating said granules to a temperature below the melting. point 01 the granules with gases containingsulphur dioxide and having an oxygen content less than air.

4. A process for converting finely divided lead ores into lump form for metallurgical treatment on the ore hearth by the roasting reaction method, which comprises granulating said fine lead ores to form granules and heating said granules to a temperature below the melting point of the granules with gases containing carbon dioxide and having an oxygen content less than air.

5. A process for converting finely divided lead ores into lump form for metallurgical treatment on the ore hearth by'the roasting reaction method, which comprises granulating said fine lead ores to form granules and heating said granules to a temperature below the melting point of the granules with gases containing sulphur dioxide and carbon dioxide and having an oxygen content less than air. 1

6. A process for recovering metallic lead from finely divided lead ores which comprises agglomerating finely divided lead ores containing sulphur, heating said agglomerated lead ores to temperatures above about 200 C. and below the melting point of the agglomerate for a period of time inversely proportional to the temperature substantially without reduction of said sulphur content, and introducing said agglomerates onto an ore hearth and recovering metallic lead whereby metallic lead is recovered from finely divided lead ores without the production of an excessive amount of fines.

7. A process for recovering metallic lead from finely divided lead ores which comprises agglomerating finely divided lead ores containing sulphur, heating said agglomerated lead ores to temperatures above about 200 C. and below the melting point of the agglomerates substantiallywithout reduction of said sulphur content for a period of time inversely proportional to the temperature in the presence of gases containing carbon dioxide and having an oxygen content less than that of air, establishing a charge of said agglomerates on an ore hearth and recovering metallic lead whereby metallic lead is recovered from finely divided lead ores without the production of an excessive amount of fines.

8. A process for recovering metallic lead from finely divided lead ores which comprises agglomrecovered from finely divided lead ores without the production of an excessive amount of flue dust.

9. A process for recovering metallic lead from finely divided lead ores which comprises agglomerating finely divided lead ores containing sulphur, heating said agglomerated ores above about 200 C. and below the melting point of said agglomerates for a period of time inversely proportional to the temperature in an atmosphere having an oxygen content less than that of air and containing sulphurous anhydride, charging said agglomerates onto an orehearth and recovering metallic lead whereby metallic lead is recovered from finely divided lead ores without the production of an excessive amount of flue dust.

10. A process for recovering metallic lead from finely divided lead ores which comprises agglomerating finely divided lead ores containing sulphur, heating said agglomerated ores to a temperature above about 200 C. and below the melting point of said agglomerates for a period of time inversely proportional to said temperature, passing gases containing sulphurous dioxide and less oxygen than air through said agglomerated ores, returning at least a part of said gases after passing through said agglomerated ores to a roasting process, establishing a charge of said agglomerates on an ore hearth, roasting said agglomerated lead ore containing sulphur in the presence of said returned gases and repeating the aforesaid operations whereby metallic lead is recovered from finely divided lead ore and the sulphurous dioxide content of gases evolved during agglomeration and roasting is raised above 0.5 to 1.5%.

ll. A process for recovering metallic lead from finely divided lead ores which comprises agglomerating finely divided lead ores containing sulphur, dusting said agglomerated ores with fuel, igniting said dusted agglomerated ores and reducing said sulphur content about 10 to about 30%, establishing a charge of said ignited agglomerates onto an ore hearth and recovering metallic lead whereby the roasting reaction for the recovery of metallic lead from said ignited agglomerated lead ores having a slightly reduced sulphur content is accelerated.

12. A process for recovering metallic lead from finely divided lead ores which comprises agglomerating finely divided lead ores containing sulphur, and heating said agglomerated ores to temperatures above 200 C. and below the melting point of said agglomerates for a period of time inversely proportional to said temperature in an atmosphere containing less oxygen than air but containing sufiicient oxygen to cause superficial oxidation of said sulphur in said agglomerated ores at the surface of said agglomerates thereby forming a shell of great mechanical strength on the surface of said agglomerates capable of maintaining the oxidation of said sulphur at a small amount during said heating and subsequently assisting in said roasting on the ore hearth, establishing a charge of said agglomerates on an ore hearth and recovering metallic lead whereby metallic lead is recovered from finely divided lead ores without the formation of an excessive amount of fiue dust.

KURT RUDOLF GfiHRE.

Patent No. 2,116,679-

KURT RUDOLF seams.-

It is hereby certified that error appears in the printed specification of the abovenumbered patent requiring correction as follows: Page 11,, first column, line h2,'for the numeral "0.05" read O.5; and that the said Let ters Patent should be read with this correction therein that the same may conform to the record of the ease in the Patent Office.

Signed and sealed this 9th day of August, A. 1;. 19 8.

(Seal) Leslie Frazer Acting Commissioner of Patents.

9. A process for recovering metallic lead from finely divided lead ores which comprises agglomerating finely divided lead ores containing sulphur, heating said agglomerated ores above about 200 C. and below the melting point of said agglomerates for a period of time inversely proportional to the temperature in an atmosphere having an oxygen content less than that of air and containing sulphurous anhydride, charging said agglomerates onto an orehearth and recovering metallic lead whereby metallic lead is recovered from finely divided lead ores without the production of an excessive amount of flue dust.

10. A process for recovering metallic lead from finely divided lead ores which comprises agglomerating finely divided lead ores containing sulphur, heating said agglomerated ores to a temperature above about 200 C. and below the melting point of said agglomerates for a period of time inversely proportional to said temperature, passing gases containing sulphurous dioxide and less oxygen than air through said agglomerated ores, returning at least a part of said gases after passing through said agglomerated ores to a roasting process, establishing a charge of said agglomerates on an ore hearth, roasting said agglomerated lead ore containing sulphur in the presence of said returned gases and repeating the aforesaid operations whereby metallic lead is recovered from finely divided lead ore and the sulphurous dioxide content of gases evolved during agglomeration and roasting is raised above 0.5 to 1.5%.

ll. A process for recovering metallic lead from finely divided lead ores which comprises agglomerating finely divided lead ores containing sulphur, dusting said agglomerated ores with fuel, igniting said dusted agglomerated ores and reducing said sulphur content about 10 to about 30%, establishing a charge of said ignited agglomerates onto an ore hearth and recovering metallic lead whereby the roasting reaction for the recovery of metallic lead from said ignited agglomerated lead ores having a slightly reduced sulphur content is accelerated.

12. A process for recovering metallic lead from finely divided lead ores which comprises agglomerating finely divided lead ores containing sulphur, and heating said agglomerated ores to temperatures above 200 C. and below the melting point of said agglomerates for a period of time inversely proportional to said temperature in an atmosphere containing less oxygen than air but containing sufiicient oxygen to cause superficial oxidation of said sulphur in said agglomerated ores at the surface of said agglomerates thereby forming a shell of great mechanical strength on the surface of said agglomerates capable of maintaining the oxidation of said sulphur at a small amount during said heating and subsequently assisting in said roasting on the ore hearth, establishing a charge of said agglomerates on an ore hearth and recovering metallic lead whereby metallic lead is recovered from finely divided lead ores without the formation of an excessive amount of fiue dust.

KURT RUDOLF GfiHRE.

Patent No. 2,116,679-

KURT RUDOLF seams.-

It is hereby certified that error appears in the printed specification of the abovenumbered patent requiring correction as follows: Page 11,, first column, line h2,'for the numeral "0.05" read O.5; and that the said Let ters Patent should be read with this correction therein that the same may conform to the record of the ease in the Patent Office.

Signed and sealed this 9th day of August, A. 1;. 19 8.

(Seal) Leslie Frazer Acting Commissioner of Patents. 

